It is my understanding that one should not defrag an SSD.
SSDs operate differently from regular disks. No slowdown due to head-movements when reading fragmented consecutive data, but a slowdown due to wear-leveling algorithms that try to balance the limited number of writes to all memory locations evenly. So rewriting the data of a catalog will gradually slow down performance of the SSD. The gradual slow down can be 'fixed' by issuing a TRIM command
with appropriate tools (e.g. O&O software's Defrag Professional
, or similar alternatives).
If my LR5 catalog is on an SSD and I backup to a different drive, will optimization of the catalog upon exiting and backing up LR5 in any way harm or adversely affect the SSD (which contains all LR5 files except the images and the backups)?
It will gradually slow down SSD performance, I do not know if it helps getting the data cleaned up in other ways that might benefit performance but I somewhat doubt it, on an SSD that is.